The Masters Slow-DownThe obvious answer is that we’re aging. But “aging” is a catch-all phrase, a reason to put more candles on the birthday cake. If we knew which specific aspects of aging affected our running performance, we could adjust our training to combat the slow-down.

Posters to a recent message board thread on LetsRun.com debated this issue, breaking it into its simplest components: speed and endurance. Many posters believed that aging runners lose their top speed first. “I’d be surprised if masters sprint records didn’t drop off more than masters distance records,” wrote Heard Through The Grapevine. Others disagreed. “It is a myth that one loses [speed] more easily than endurance,” wrote Sir Lance-Alot. “[Masters] stop training sprint/power ability, and that is why they lose it.”

As it turns out, masters athletes don’t lose top speed faster than endurance. A calculation of percent change in men’s and women’s masters world records between the 40-44 and 70-74 age groups – focusing on three distances – gives this result:

Both male and female masters sprinters slow less than masters distance runners, which would seem to indicate that we lose endurance before speed – except we don’t.

You see, we begin to lose skeletal muscle mass at around age 25. But it turns out that our slow-twitch (endurance) muscle fibers are resistant to age-related atrophy. Instead, it’s our fast-twitch (speed) muscle fibers that disappear at a rate of up to 1% per year!

On the surface, this makes no sense. If we lose fast-twitch fiber while retaining slow twitch, we should expect to maintain endurance while our speed declines. Yet the percent change in masters world records shows the opposite to be true. How can this be?

The answer won’t please most masters distance runners. Because the answer is that sprinters train smarter and with greater intensity than their endurance peers.

The Value of Speed Training“[In] groups of equally trained distance runners,” writes exercise physiologist Tim Noakes in Lore of Running, “I suspect that the best runners at any longer distance are those who are fastest over distances from 100 to 800 [meters] and whose brains and muscles are also highly fatigue resistant.”

In other words, all other things being equal among distance runners, the fastest sprinter in the group wins the race. It’s not enough for masters distance runners to fill their training logs with volume, tempo, race-pace intervals, and the occasional session of post-run strides. If we don’t use our fast twitch fiber (Type IIa and IIx), we lose it.

And fast-twitch fiber isn’t just about sprint speed. It’s a primary component (along with hip and knee range of motion) of stride length. Studies over the past 20 years have all come to the same conclusion: As we age, our stride frequency remains the same, but our stride length decreases – an average of 40% by the time we reach our 70s and 80s. Slowing the decrease in stride length through speed training simultaneously slows the decline in our distance race performance. Otherwise, we’d need almost twice the stride frequency to maintain our mile pace from age 40 to age 80.

The good news is that we can reverse much of the damage. A 2009 study found that sprint training led to “significant gains in maximal and explosive strength and improvements in force production during running.” With proper training, we can rebuild our stride, recapture our speed, and maintain both as we age.